Administration of in vivo-released lymphokines to a mouse has inhibited the growth in vivo and in vitro (a) of such intracellular pathogens as Candida albicans and (b) of tumors. Manipulation of the release of the lymphokines results in variations in cell-mediated immunity. Delayed hypersensitivity is regulated at least in part, by splenic B-cells, as indicated by adoptive transfer of skin hypersensitivity and by inhibition in vitro of cell replication. BIBLIOGRAPHIC REFERENCES: R. Neta and S. B. Salvin. 1976. T & B lymphocytes in the regulation of delayed hypersensitivity. J. Immunol. 117, 2014-2020. S. B. Salvin, J. S. Youngner, J. Nishio, and R. Neta. 1976. A tumor-inhibiting lymphokine from tuberculous mice. Ann. N.Y. Acad. Sci., 276, 369-372.